The present invention relates to the installation of cables, such as optical fibre units, wires, electrical cables or the like. More specifically, but not exclusively, the present invention relates to the blowing of fibre unit cables through pre-laid conduits.
Optical fibres are widely used within telecommunication systems for high-speed information transfer. A fibre unit, which could comprise a single optical fibre, or a bundle of optical fibres, is commonly installed into a protective optical conduit comprising optical fibre tubes, which have already been laid along the desired route, usually as a continuous span between convenient access points such as surface boxes or inspection chambers.
In this description, references to “cables” shall include where the context permits, individual optical fibres and fibre units as well as cables comprising such fibres and fibre units. “Conduits” shall include tubes and tube bores, but in the main refers to the route or path populated or to be populated by a fibre cable, and where the route comprises a number of tubes, the entire length of the route.
The conduits typically are made of plastic, each with a typical inner diameter of 3 to 6 mm or more, and are usually provided in a bundle comprising up to 24 or more tubes, which are held together within a protective outer sheath. Each fibre conduit tube can receive at least one fibre unit comprising one or more individual optical fibres. Large numbers of conduits—and bundles of conduits—are pre-installed across the access network and the distribution network between the local exchanges and the customer premises in a branching network system. With the advent of fibre to the premises (FTTP), the conduits will further extend to and into commercial and residential premises. Indeed it is a fundamental part of the push to FTTP in e.g. the UK that substantially all the network comprises optical fibre, extending from the core network to as many end customers as possible. To achieve this, optical fibre installation needs to be speedy, cost- and effort-efficient.
In the vast majority of cases, a dedicated path is described between two points with a single length of conduit tube. In an exceptional case, the conduit path may comprise a number of lengths of physically separate conduit tubes which are connecterised together in series with tube connectors. Choosing the correct conduit tube at the installation should in the normal case, result in the fibre unit emerging at the other end.
Problems however may arise which result in the fibre unit not reaching the correct destination. During installation, the operator is usually presented with a large number of conduit tubes, which could result in a mistake in identifying the correct conduit, especially if the operator is working in adverse conditions down a manhole or in poor lighting. This may be so even where conduits are coloured coded which helps to direct the operator to the correct conduit.
There is also the possibility that a conduit route is wrongly mapped in the records used by the operator so that one end of the conduit does not lead to the correct destination. Where the path comprises a number of tube lengths connectorised together in series, yet another problem may lie in broken connections between lengths of conduit tubes within the network, so that the fibre unit may get lost within the system during installation and never emerge at the destination. Yet another issue may be the possibility that the fibre unit, during installation, could be impeded by an imperfect connector or a tight bend or some other source of friction in the conduit, and again never emerge at the destination.
For any of these or other reasons, the fibre unit will emerge in the wrong place, or not at all. Add to that some uncertainty about the exact length of the conduit route down which the fibre unit is being installed, so that the operator cannot even accurately know in a timely manner when something has gone wrong.
One method of installing fibre units into the conduits is by pulling them through the conduits. However, the tension induced can cause damage to the fibre units and impair their operating performance. A known alternative method is the “blown fibre” technique whereby a compressed fluid such as compressed air is used to convey, or “blow”, a fibre unit along a conduit from one end.
Currently, installing fibre units using the blown fibre method requires at least two operators: one situated at the head end of the conduit, where during installation air and the fibre unit are installed into the mouth of the conduit, and one at the remote end of the conduit, where air and the fibre unit emerge from the mouth of the conduit. The second remote end operator is required because the remote end is often some distance away—up to a kilometer or more—from the head end. The operator at the head end is therefore unable to know the status of the remote end during an installation without a second operator located there.
The head end operator monitors and operates a fibre installation mechanism—known in the art as a “blowing head”—that feeds the optical fibre into the conduit and controls the supply of compressed air. He starts the process by directing air into the mouth of the head end conduit. If the air is directed into the correct conduit, the remote end operator will sense the arrival of the air with an air flow meter temporarily connected to the end of the conduit, or more simply by feeling the air flow exiting the conduit against his hand if the air flow is sufficiently high. He then communicates this to the head end operator by radio or other means, to confirm to the head end operator that he is applying air to the correct conduit. The head end operator then introduces the fibre unit into the conduit and blows it through to the remote end of the conduit, whereupon the remote end operator advises his colleague on its arrival. The head end operator then turns off the air supply and the blowing head, and the process is complete.
This process is labour-intensive as a minimum of two operators must work on a single installation. The head end operator needs to be skilled in the operation of the blowing head, while the remote end operator is required to alert his colleague to the status of the installation at the remote end.
Methods whereby a single operator at the head end of a conduit can detect the arrival of an optical fibre at the remote end of the conduit are known.
In the simplest method, the length of the conduit route is known, allowing the operator to know that the fibre has (probably) arrived at the remote end when the required length of fibre unit has been played out. This relies on the map record of conduit route being up to date and accurate, and presumes a completely smooth and obstruction-free conduit route. Neither of these can be guaranteed in practice.
Another known practice is to install at the remote end of the conduit a barrier of porous material such as an “airstone” which is placed at the remote end of the conduit, which will allow air through but which will stop further progress of the fibre unit. This cease in progress is detected by the blowing head which then stops further ingress. However even when the progress of the fibre has ceased, the operator at the head end cannot be certain that the fibre unit has reached the porous barrier at the end of the conduit, or if instead the fibre unit is caught on an obstruction at some point along the length of the conduit.
As described in WO9103756, a solution is to position a light source at the remote end of the conduit and a light detector is positioned at the head end. The arrival of the optical fibre at the remote end is indicated by the detection of light by the detector at the head end. One problem with this method is that an early, or “false”, indication of the arrival of the optical fibre may occur if stray light is inadvertently introduced into the conduit at a location between the head end and remote end, e.g. at an open inspection chamber. This method also relies on adequate light being coupled into the advancing end of the optical fibre to be detected by the detector, however the coupling process is inefficient and is further degraded in proportion to the length of the optical fibre due to normal attenuation properties, so this method may not be practicable on long lengths of optical fibre. A second method described in this document uses a previously installed optical fibre to create part of a light “circuit” with the blown optical fibre. This method is not as suitable for installing the first optical fibre in a conduit. Furthermore, any previously installed fibre units may be carrying live traffic and so would not be available to use for the installation of additional fibres.
Another known method is to use a blowing head such as that described in WO/9812588, which is configured to stop driving the fibre unit when it senses that fibre movement within the conduit is slowing down or stopping owing to an obstruction. When used in conjunction with a porous airstone at the remote end, the fibre unit would stop moving when it reaches the destination end. However, as the sealed-off end is just one type of obstruction the fibre unit may encounter on the conduit route, this method fails to positively identify when the fibre unit has reached and emerged from the conduit at the remote end without travelling to the remote end for a visual inspection.
Accordingly, in a general aspect, the present invention provides methods and devices for aspects relating to the installation of cables such as fibre units into conduit tubes, in particular, allowing a single operator to operate substantially on his own to determine if air fed into a conduit is reaching its intended destination, and/or if and when the fibre unit fed into the conduit has reached its destination. The invention can be used where the operator has to choose one of a number of conduits, or where there is a single conduit but where it is desirable to unambiguously confirm that the air and fibre unit reaches the intended destination.
A first aspect of the invention provides a method for use in connection with installing a cable into a conduit having a first conduit end and a second conduit end, comprising the steps of                providing the cable with a metallic attribute,        providing within or proximate to the conduit, sensing means for sensing the metallic attribute,        introducing the cable into the first conduit end and driving it towards the second conduit end, and        detecting that the sensing means has sensed the metallic attribute by sensing a change in inductance levels of the sensing means.        
By using this method, a fibre bead detection system can be set up to send a signal to an operator situated at the head end of the cable tube installation to indicate or confirm if and when the fibre unit fed into the conduit at the head end has arrived at the remote end. The metallic attribute can be an inherent part or property of the cable, although conveniently it is provided in the invention in the form of a metal sleeve or a bead capable of actuating the sensor, which can be placed at any point along the length of the cable. If the method is to serve to signal arrival of the fibre at the remote end, the actuator can be positioned at the advancing end or tip of the cable.
A variety of metals can be sensed or detected by changes in inductance levels of a sensor such as an induction coil. In a preferred version of the invention, a change in the frequency oscillation of an LC oscillator is sensed.
The skilled person would also appreciate that the method can be used to detect the electromagnetic actuator itself, or any object or article to which the actuator is attached.
A second aspect of the invention provides a device for use in connection with installing a cable provided with a metallic attribute, into a conduit having a first conduit end and a second conduit end, comprising
sensing means for sensing the metallic attribute, and
detecting means to detect that the sensing means has sensed the metallic attribute by sensing a change in inductance levels of the sensing means.
The device is preferably adapted to be used with a metallic actuator. If it is used to detect fibre unit arrival, it should preferably be coupled to the conduit at its remote end. In such a case, one embodiment of the invention is a device with a bore communicating with the conduit so that the fibre can enter the bore to allow for its presence to be sensed by the detecting means.
Alternatively, the device can be fitted anywhere else along the conduit, to detect the fibre coupled to the actuator, or else to track the movement or location of the fibre in a network of conduits. Thus, the device of the invention can be used for tracking or detection in other applications or contexts where an item with a metallic property or attribute is moving within a conduit or container or even outside containment means. The device can also be configured for the detection of speed of movement of the metallic actuator.
Preferably, the device includes means to contain the actuator in such a way that the detecting means is as close as possible for greater sensitivity. The sensing means can comprise any means sensitive to a metallic attribute, but in the embodiment it can comprise an LC oscillator including an inductive loop.
A third aspect of the invention provides a device for use in connection with installing a cable into a conduit having a first conduit end and a second conduit end, the cable including sensing means for sensing a metallic attribute, comprising
a metallic actuator, and
detecting means to detect that the metallic actuator has been sensed by the sensing means by sensing a change in inductance levels of the sensing means.
It is within the scope of the invention for the sensing means and the actuator to be located in the other's place i.e. the sensing means can be associated with the fibre unit cable, and the actuator positioned where it is desired to sense the presence of the fibre unit or other object to which the actuator is coupled.
A fourth aspect of the invention provides a metallic actuator for use in connection with installing a cable into a conduit having a first conduit end and a second conduit end,
the actuator comprising a body for securing to the cable,
and suitable for use with a device comprising
sensing means for sensing the metallic attribute, and
detecting means to detect that the sensing means has sensed the metallic attribute by sensing a change in inductance levels of the sensing means.
As noted above, this can be any device having the necessary metallic attribute to allow it to be sensed by the sensing device, and which can be coupled to the fibre unit or other object. Thus, although it is described below as a bead connected to the advancing tip of the fibre, it could for example, take the form of a sleeve, or an adhesive strip or sheet, or some kind of substance which can be painted on the object to be sensed. The skilled person would understand that the invention includes the sensing of the actuator itself moving though the medium (which in a blown fibre installation comprises air), so the actuator could be used to sense the presence, movement and speed of the medium at a particular section within the conduit, or conduit network, as the case may be.
A fifth aspect of the invention provides a metal sensor for use in connection with installing a cable into a conduit having a first conduit end and a second conduit end, the sensor comprising a body for securing to the cable,
and being suitable for use with a device comprising
a metallic actuator, and
detecting means to detect that the metallic actuator has been sensed by sensing a change in inductance levels of the sensor.
This aspect of the invention is a sensor which can be coupled to the fibre unit or other object, which can be used with the device of the third aspect of the invention as described above. Used together, the sensor and the actuator provide the necessary change in the sensor and/or actuator to allow an operator to detect the presence of the actuator and thus the fibre unit or other object to which the sensor is connected to.
A sixth aspect of the invention provides an installation for installing a cable using an air flow into a conduit having a first conduit end and a second conduit end, comprising
an air source to introduce air into the conduit at the first conduit end,
driving means to mechanically drive the cable through the conduit, and
cable presence detection means comprising                a device including                    sensing means for sensing a metallic attribute of the cable, and            detecting means to detect that the sensing means has sensed the metallic attribute by detection of a change in the inductance levels of the sensing means, and                            a metallic actuator comprising a body for securing to the cable.                                                
A blown fibre installation includes other apparatus: an air compressor to supply pressurised air into the conduit, and a blowing head including drive wheels to mechanically drive the fibre unit into the conduit. The devices of the invention can be advantageously used in such an installation to provide an operator with information about the location of the fibre unit or the actuator.
A seventh aspect of the invention provides a method for use in connection with installing a cable using an air flow into a conduit having a first conduit end and a second conduit end, comprising    (i) a method to detect the air flow at the second conduit end, comprising the steps of            introducing the air flow into the conduit,        introducing a signal into the conduit, or into a bore communicating with the conduit, and        detecting a change in a property of the signal caused by movement of the air flow, and            (ii) a method comprising the steps of            providing the cable with a metallic attribute,        providing within or proximate to the conduit, sensing means for sensing the metallic attribute,        introducing the cable into the first conduit end and driving it towards the second conduit end, and        detecting that the sensing means has sensed the metallic attribute by detection of a change in the inductance levels of the sensing means.        
By using this method, an operator can first obtain a positive indication that air is flowing to and from the correct remote end of the conduit by using a phase shift' detection method, then immediately follow up with feeding the fibre unit into the identified conduit at the head end, and upon learning that the fibre unit fitted with the actuator has reached the far end, the installation session can be terminated. The method can also be used to track air or fibre location within the conduit or network of conduits, as well as to sense speeds of movement of the air and/or fibre unit.
An eighth aspect of the invention provides a device for use in connection with installing a cable using an air flow into a conduit having a first conduit end and a second conduit end, comprising    (i) a device to detect of the air flow at the second conduit end, comprising            a transmitter for transmitting a signal into the conduit, and        a detector to detect a change in a property of the signal caused by movement of one or both of the air flow and the cable, and            (ii) a device comprising            sensing means for sensing the metallic attribute, and        detecting means to detect that the sensing means has sensed the metallic attribute by detection of a change in the inductance levels of the sensing means.        
The device in his aspect incorporates the means to sense and detect a phase shift created by movement of air or of the fibre unit within the conduit, as well as an electromagnetic change brought about by the proximity of the electromagnetic sensor and electromagnetic actuator.
A further aspect of the invention provides an installation for installing a cable into a conduit having a first conduit end and a second conduit end, comprising    (i) an installation comprising            an air source to introduce air into the conduit at the first conduit end,        driving means to mechanically drive a cable through the conduit,        a transmitter for transmitting a signal into the conduit, and        a detector to detect a change in a property of the signal caused by movement of one or both of the air flow and the cable, and            (ii) an installation comprising            an air source to introduce air into the conduit at the first conduit end,        driving means to mechanically drive the cable through the conduit, and        cable presence detection means comprising either a device including sensing means for sensing the metallic attribute, and        detecting means to detect that the sensing means has sensed the metallic attribute by detection of a change in the inductance levels of the sensing means,        used in conjunction with a metallic actuator comprising        detecting means to detect that the sensing means has sensed the metallic attribute by detection of a change in the inductance levels of the sensing means.        
The installation for a blown fibre installation advantageously includes the devices and means for air and the fibre unit to be fed into the conduit at the head end, and for such air and fibre unit to be detected at the remote end.